Filter member and oxygenator using same

ABSTRACT

A filter member used in an oxygenator is constructed to provide improved contact with a hollow fiber membrane bundle and to capture bubbles contained in blood. The filter member possesses elasticity at least in the circumferential direction to allow the inner circumference of the filter member to be increased from a natural non-expanded state prior to placement on the hollow fiber membrane bundle to an expanded state in which the inner circumference of the filter member is increased when placed on the hollow fiber membrane bundle. The filter member is constructed to satisfy the condition 0.5≦L 2 /L 1 &lt;1, wherein L 1  represents the outer circumference of the hollow fiber membrane bundle and L 2  represents the inner circumference of the filter member in the natural non-expanded state.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. patent application Ser. No.13/789,856 filed Mar. 8, 2013, now allowed, which is a divisional ofU.S. patent application Ser. No. 11/727,608 filed Mar. 27, 2007, nowU.S. Pat. No. 8,425,838 issued Apr. 23, 2013, and claims priority under35 U.S.C. §119 to Japanese Patent Application No. 2006-089283 filed Mar.28, 2006, the disclosures of all of which are incorporated herein byreference in their entirety.

TECHNICAL FIELD

The present invention generally pertains to medical devices. Moreparticularly, the present invention relates to a filter member and anoxygenator incorporating a filter member.

BACKGROUND DISCUSSION

U.S. Pat. No. 6,503,451 discloses an oxygenator constructed for gasexchange that utilizes a multiplicity of hollow fiber membranes. Thisoxygenator includes a housing, a hollow fiber membrane bundle receivedin the housing, blood inlet and outlet ports, and gas inlet and outletports. The oxygenator effects gas exchange (i.e., oxygenation andcarbon-dioxide removal) between blood and gas through the hollow fibermembranes.

The construction of this oxygenator makes it susceptible to thepossibility that bubbles will become mingled with the blood passingthrough the blood inlet port. In such a case, it would be desirable toremove the bubbles by virtue of the hollow fiber membrane bundle.

However, the hollow fiber membrane bundle is not fabricated with theintention of removing bubbles, but rather is designed for efficient gasexchange. Hence, the hollow fiber bundle is not well suited to beingable to sufficiently effect bubble removal. Thus, it is possible thatbubbles remaining in the blood exiting through the blood outlet portwill be conveyed downstream of the oxygenator. For this reason, it isknown to use an arterial filter for bubble removal on the arterial linefrom the oxygenator to the patient.

SUMMARY

According to one aspect, an oxygenator comprises a housing, a hollowfiber membrane bundle comprised of a plurality of gas-transmissivehollow fiber membranes each possessing a lumen, a gas inlet portcommunicating with the lumens of the hollow fiber membranes to introducean oxygen-containing gas into the lumens, a gas outlet portcommunicating with the lumens of the hollow fiber membranes, a bloodinlet port communicating with a blood flow path that is exterior of thehollow fiber membranes in the housing, a blood outlet port communicatingwith the blood flow path, and a filter member adapted to be positionedin the housing in surrounding relation to the outer peripheral surfaceof the hollow fiber membrane bundle. The filter member possessescircumferential elasticity allowing the inner circumference of thefilter member to be increased from a natural non-expanded state prior toplacement on the hollow fiber membrane bundle to an expanded state inwhich the inner circumference of the filter member is increased whenplaced on the hollow fiber membrane bundle. The inner circumference ofthe filter member in the natural non-expanded state is less than theouter circumference of the hollow fiber membrane bundle.

In accordance with another aspect, an oxygenator comprises a housing, ahollow fiber membrane bundle positioned in the housing and comprised ofa plurality of integrated hollow fiber membranes that are transmissiveto gas and that each include a lumen, a gas inlet and a gas outletrespectively positioned upstream and downstream of the lumens of thehollow fiber membranes, a blood inlet and a blood outlet respectivelypositioned upstream and downstream of a blood passage that is exteriorof the hollow fiber membranes, and a cylindrically shaped filter memberarranged in close contact with the outer periphery of the hollow fibermembrane bundle and structured with a thin thread. The filter memberpossesses circumferential elasticity allowing the filter member to becircumferentially expanded when placed on the hollow fiber membranebundle, and the thin thread comprising the filter member is arranged ina direction not coincident with a circumferential direction of thefilter member.

According to another aspect, a filter arrangement is configured to bepositioned in the housing of an oxygenator and comprises a cylindricallyshaped filter member in combination with a hollow fiber membrane bundlecomprised of a plurality of integrated hollow fiber membranes that aretransmissive to gas. The filter member is configured to be arranged overan outer periphery of the hollow fiber membrane bundle to closelycontact the outer periphery of the hollow fiber membrane bundle. Thefilter member possesses circumferential elasticity allowing the innercircumference of the filter member to be increased from a naturalnon-expanded state prior to placement on the hollow fiber membranebundle to an expanded state in which the inner circumference of thefilter member is increased when placed on the hollow fiber membranebundle. With the outer circumference of the hollow fiber membrane bundlebeing represented by L1 and the inner circumference of the filter memberin the natural non-expanded state being represented by L2, the condition0.5≦L2/L1<1 is satisfied.

Another aspect involves an oxygenator comprising a housing, a hollowfiber membrane bundle comprised of a plurality of integratedgas-transmissive hollow fiber membranes each possessing a lumen, a gasinlet port communicating with the lumens of the hollow fiber membranesat an upstream side of the lumens to permit an oxygen-containing gas tobe introduced into the lumens, a gas outlet port communicating with thelumens of the hollow fiber membranes at a downstream side of the lumens,a blood inlet port communicating with a blood flow path that is exteriorof the hollow fiber membranes in the housing, a blood outlet portcommunicating with the blood flow path, and a filter member positionedin the housing in surrounding relation to the outer peripheral surfaceof the hollow fiber membrane bundle. The filter member is comprised of aplurality of threads forming a mesh, and the plurality of threads forman angle other than zero degrees with a plane perpendicular to thelongitudinal axis of the filter member so that the filter memberpossesses circumferential elasticity allowing an inner circumference ofthe filter member to be increased from a natural non-expanded stateprior to placement on the hollow fiber membrane bundle to an expandedstate in which the inner circumference of the filter member is increasedwhen placed on the hollow fiber membrane bundle. The outer circumferenceL1 of the fiber membrane bundle is dimensioned relative to the innercircumference L2 of the filter member in the natural non-expanded stateso that L2/L1<1.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a perspective exploded view of an embodiment of a filtermember disclosed herein.

FIG. 2 is a plan view, partly broken away, of an embodiment of anoxygenator disclosed herein.

FIG. 3 is a left side view of the oxygenator shown in FIG. 2 as viewedin a direction of arrow III.

FIG. 4 is a cross-sectional view of the oxygenator taken along thesection line IV-IV in FIG. 3.

FIG. 5 is a cross-sectional view of the oxygenator taken along thesection line V-V in FIG. 2.

FIG. 6 is an enlarged cross-sectional view of a portion of theoxygenator showing the manner of fixing a hollow fiber membrane andfilter member to a partitioning wall.

FIG. 7 is a plan view, partly broken away, showing the manner in whichthe hollow fiber membranes are arranged in the disclosed embodiment.

FIG. 8 is a cross-sectional view similar to FIG. 5 illustrating anotherembodiment of the oxygenator that includes a different housing.

FIG. 9 is a perspective view of the housing used in the oxygenator shownin FIG. 8.

DETAILED DESCRIPTION

FIGS. 2-7 illustrate one embodiment of an oxygenator, including a filtermember, as disclosed herein. In the illustrated embodiment shown inFIGS. 2-7, the oxygenator possesses a nearly circular cylindricalexterior form. In the disclosed embodiment, the oxygenator 1 is a heatexchanger-equipped oxygenator which includes an interiorly positioned(centrally positioned) heat exchange part (heat exchanger) 1B thatperforms heat exchange with blood, and an oxygenator part 1A providedoutwardly of the heat exchange part 1B that performs gas exchange withblood.

The oxygenator 1 comprises a housing 2 in which is received theoxygenator 1A and the heat exchange part 1B. Within the housing 2, theheat exchange part 1B is further received in a heat exchanger housing 5.By way of the heat exchanger housing 5, the heat exchange part 1B isfixed at both of its ends to the housing 2.

The housing 2 is comprised of a housing body 21 possessing a circularcylindrical form (hereinafter referred to as “cylindrical housingbody”), a first dish-shaped header (upper lid) 22 closing a left-endopening of the cylindrical housing body 21, and a second dish-shapedheader (lower lid) 23 closing a right-end opening of the cylindricalhousing body 21.

The cylindrical housing body 21, the first header 22 and the secondheader 23 are formed of a resin material, e.g., polyolefin such aspolyethylene or polypropylene, an ester resin (e.g. polyester such aspolyethylene terephthalate or polybutylene terephthalate), a styreneresin or polycarbonate, ceramics material of various kinds or a metalmaterial. The first and second headers 22, 23 are secured in aliquid-tight manner to the cylindrical housing body 21 by joining, forexample through fusion or an adhesive.

The outer periphery of the cylindrical housing body 21 is formed with atubular blood outlet port 28. The blood outlet port 28 projects in adirection nearly tangential to the outer peripheral surface of thecylindrical housing body 21.

A blood inlet port 201 and a gas outlet port 27 are formed on firstheader 22. The blood inlet port 201 and gas outlet port 27 are tubularin form and project from the first header 22.

A gas inlet port 26, a gas outlet port 29, a heating-medium inlet port202 and a heating-medium outlet port 203 are formed on the second header23. The gas inlet port 26, gas outlet port 29, heating-medium inlet port202 and heating-medium outlet port 203 are tubular in form and projectfrom the second header 23.

It is to be understood that the overall shape of the housing 2 need notbe perfectly circular cylindrical.

As shown in FIG. 4, the oxygenator part 1A is received within thehousing 2 and possesses a circular cylindrical form extending along theinner peripheral surface thereof. The oxygenator 1A comprises a hollowfiber membrane bundle 3 that is nearly cylindrical in its overall form,and a filter member 4 serving as bubble catching means provided aroundthe hollow fiber membrane bundle 3. The hollow fiber membrane bundle 3is comprised of a plurality of hollow fiber membranes 311, preferablygas-transmissive hollow fiber membranes.

The hollow fiber membranes 311 and the filter member 4 are fixed at bothof their lengthwise ends (axial ends) by way partitioning walls 8, 9 soas to be fixed relative Lo the inner surface of the cylindrical housingbody 21.

Each of the partitioning walls 8, 9 possesses a ring-shaped form asviewed in plan. The partitioning walls 8, 9 are formed from a pottingmaterial, e.g., polyurethane or silicone rubber.

The hollow fiber membrane bundle 3 can have a construction similar tothat described in U.S. Pat. No. 6,503,451. Generally describing theconstruction of the hollow fiber membrane bundle 3 as shown in FIG. 7,the hollow fiber membranes 311 forming the hollow fiber membrane bundle3 are spread around the outer periphery of a cylindrical core and arelaid out in a multi-layered manner. The hollow fiber membrane bundlescan be wound in a reel-type form over the cylindrical core. The hollowfiber membrane bundle 3 has a plurality of crosswinds 3 b, where thehollow fiber membranes 311 cross each other at and around the lengthwisecentral part of the cylindrical core. The crosswinds 3 b are arranged sothat the radially adjacent i.e., in the thickness-wise direction of thebundle) ones do not overlap one another. Namely, the adjacent crosswindsare located in different positions along the hollow fiber membranebundle 3 so that a crosswind 3 b is not located directly on, inoverlapping relation, to another crosswind 3 b. This helps avoid theoccurrence of a partial projection and a short-circuiting of blood dueto overlapping crosswinds 3 b.

In the event a projection is partially caused in the outer peripheralsurface of the hollow fiber membrane bundle 3 by overlapping crosswinds3 b of the hollow fiber membranes, the contact of the filter member 4with the hollow fiber membrane bundle may be reduced, or the flow ofblood downstream of the filter member 4 may be partially impeded. Byreducing the overlap of crosswinds 3 b, the possibility of such aproblem can be reduced or avoided, thus allowing for good bubble removalcapabilities and gas exchange.

Within the housing 2, the hollow fiber membranes 311 are exposed betweenthe partitioning walls 8, 9. A blood passage or blood flow path 33 isformed exterior of the hollow fiber membranes 311. That is, the bloodpassage or blood flow path 33 is arranged at gaps between the hollowfiber membranes 311 as shown in FIG. 6.

A blood inlet space 24 that is circular cylindrical in form existsupstream of the blood passage 33 (i.e., at a position closer to theupstream surface of the hollow fiber membrane bundle 3). The blood inletspace 24 is located between the oxygenator part 1A and the heat exchangepart 1B so that blood from the blood inlet port 201 can enter the bloodinlet space 24. The blood inlet space 24 extends around the heatexchange housing 5. That is, the blood inlet space 24 is between theouter peripheral surface of the heat exchange housing 5 and the innerperipheral surface of the hollow fiber membrane bundle 3 as shown inFIG. 4.

Blood which has been heat-exchanged and which enters the blood inletspace 24 is able to flow into the blood inlet space 24 in both thecircumferential and lengthwise directions, thus reaching the entirety ofthe blood inlet space 24. This makes it possible to transfer the bloodefficiently from the heat exchange part 1B to the oxygenator part 1A.

A spacer may be provided in the blood inlet space 24 in order tomaintain the gap between the heat exchanger housing 5 and the hollowfiber membrane bundle 3.

At a downstream portion of the blood passage 33 (i.e., at a positioncloser to the downstream surface of the hollow fiber membrane bundle 3),a circular cylindrical gap is formed between the outer peripheralsurface of the filter member 4 (described in more detail below) and theinner peripheral surface of the cylindrical housing body 21 to form ablood outlet space 25. A blood outlet is thus provided by the bloodoutlet space 25 and the blood outlet port 28 communicating with theblood outlet space 25. The blood outlet space 25 provides a space wherethe blood transmitted the filter member 4 is allowed to flow(particularly in a whirling flow) toward the blood outlet port 28 sothat the gas-exchanged blood can smoothly exit to the outside of thehousing 2.

The hollow fiber membrane bundle 3, the filter member 4 and the bloodpassage 33 are present between the blood inlet space 24 and the bloodoutlet space 25.

Though not especially limited in this regard, the hollow fiber membranebundle 3 preferably has a thickness (radial dimension in FIG. 4) ofapproximately 2-50 mm, more preferably approximately 3-30 mm, furtherpreferably approximately 4-20 mm.

The hollow fiber membranes 311 are, in the disclosed embodiment,constituted by porous hollow fiber membranes (porous gas-exchange film).The porous hollow fiber membranes to be used can have an inner diameterof approximately 100-1000 μm, a wall thickness of approximately 5-200 μmand more preferably 10-100 μm, a porosity of approximately 20-80% andmore preferably approximately 30-60%, and a pore size (average) ofapproximately 0.01-5 μm and more preferably approximately 0.01-1 μm.

The material forming the hollow fiber membranes 311 is preferably ahydrophobic polymer material, e.g. polypropylene, polyethylene,polysulfone, polyacrylonitrile, polytetrafluoroethylene or polymethylpentane. Polyolefin resin is preferred, and polypropylene is morepreferred. Pores are preferably formed in a film (a wall of the film) bystretching or solid-liquid phase separation.

The length (effective length) of the hollow fiber membranes 311 is notparticularly limited, but is preferably approximately 30-150 mm, morepreferably approximately 40-130 mm, and further preferably approximately50-110 mm.

As mentioned above, the filter member 4 is arranged downstream of thehollow fiber membrane bundle 3 and serves as bubble capture means tocapture the bubbles out of the blood. The filter member 4 capturesbubbles existing in the blood flowing in the blood passage 33. Thecaptured bubbles enter the lumens (gas passage 30) of the hollow fibermembranes 311 through the multiple pores formed in the walls of thehollow fiber membranes 311. Those bubbles are then discharged throughthe gas outlet port 27. The filter member 4 is described below in moredetail with reference primarily to FIG. 1.

The filter member 4 is formed from a sheet member (hereinafter simplyreferred to as a “sheet”) having a generally rectangular form (e.g.,parallelogram). The sheet is rolled up into a cylindrical form or shape(annular form or shape) having ends/edges joined together to form acylindrical (circular cylindrical) filter member as shown in FIG. 1. Thefilter member 4 is secured at both of its lengthwise or axial ends 43,44 (i.e., the upper and lower ends in FIG. 1) respectively by way of thepartitioning walls 8, 9 so that the filter member is fixed to thehousing 2.

The filter member 4 is positioned relative to the hollow fiber membranebundle 3 so that the inner peripheral surface of the filter member 4 isin contact with the outer peripheral surface of the hollow fibermembrane bundle 3. The filter member 4 is configured and positioned tocover nearly all of the outer peripheral surface of the hollow fibermembrane bundle 3. With this arrangement, the effective area of thefilter member 4 is increased to an extent allowing the filter member tofully exhibit the capability of capturing bubbles. In addition, becauseof the increased effective area of the filter member 4, the filtermember 4 can help prevent (suppress) the blood flow from being blockedeven if clogging occurs (e.g. adhesion of blood aggregations) in a partof the filter member 4, thus making it possible to continue theoperation of the oxygenator 1.

The filter member 4 possesses elasticity at least in the circumferentialdirection. By virtue of this, when the filter member 4 is fitted ontothe outer periphery of the hollow fiber membrane bundle 3, the fibermember 4 achieves a close fit with the outer peripheral surface of thehollow fiber membrane bundle 3.

The filter member 4 is preferably constructed relative to the hollowfiber membrane bundle 3 so that the inner circumference of the filtermember 4 in the natural state prior to placement on the hollow fibermembrane bundle 3 is less than the outer circumference of the hollowfiber membrane bundle. More specifically, the filter member 4 ispreferably constructed relative to the hollow fiber membrane bundle 3 tosatisfy the relationships described below. If the outer periphery (outercircumference) of the hollow fiber membrane bundle 3 over which thefilter member 4 is fitted is represented by the length L1 as shown inFIG. 1, and the inner periphery (inner circumference) of the filtermember 4 in the natural state in which no external force is applied (thestate in which the filter member 4 is neither expanded nor contractedcircumferentially, hereinafter referred to as the “natural state”) isrepresented by the length L2 as shown in FIG. 1, the filter member 4 ispreferably constructed so that the condition 0.5—L2/L1<1 is satisfied,preferably so that the condition 0.55≦L2/L1≦0.99 is satisfied, and morepreferably so that the condition 0.93≦L2/L1≦0.98 is satisfied. Thus,L2/L1<1. The inner circumference of the filter member mentioned aboverefers to the distance around the inner peripheral surface of the filtermember as measured at a plane perpendicular to the longitudinal axis ofthe filter member, and the outer circumference of the fiber membranebundle mentioned above refers to the distance around the outerperipheral surface of the fiber membrane bundle as measured at a planeperpendicular to the longitudinal axis of the fiber membrane bundle.

By satisfying this condition, the filter member 4 when fit over theouter periphery of the hollow fiber membrane bundle 3 is positivelyplaced into close contact with the outer peripheral surface of thehollow fiber membrane bundle 3 cooperatively with the circumferentialelasticity. As a consequence, the bubbles captured at the filter member4 are readily excluded through the hollow fiber membrane 311 locatedimmediately nearby the inner (upstream) surface of the filter member 4.Namely, the satisfaction of the condition can enhance the dischargeefficiency (removal capability) of the bubbles captured by the filtermember 4.

The filter member 4 may be, say, a mesh structure or a woven fabric, anon-woven fabric or a combination thereof. Of these, a mesh structure ispreferred, and particularly a screen mesh filter is preferred. Thisstructure makes it possible to catch bubbles more positively and to passblood easily, thus contributing to providing an oxygenator havingrelatively high blood processing efficiency and relatively excellentsustainability (i.e., is capable of operating for a relatively longtime).

Meanwhile, the filter member 4 is preferably formed by a sheet made bycrossing a weft thread (thin wire) 41 and a warp thread (thin wire) 42with each other as generally seen in FIGS. 1 and 2. Such structureincludes, by way of example, a woven fabric that is weaved plain with awarp thread 41 and a weft thread 42, a resin-made mesh (including ascreen mesh filter) formed by crossing a warp thread (resin-fibrous thinwire) 41 and a warp thread (resin-fibrous thin wire) 42 into a latticeform, and others. Such a structure can capture bubbles positively whileallowing blood to relatively easily pass, thus contributing to providingan oxygenator having relatively high blood processing efficiency andrelatively excellent sustainability (i.e., is capable of operating for along time).

The warp thread 41 and the weft thread 42 may be fixed or not fixed atpoints or areas of intersection (or may movable freely to a certainextent).

When the filter member 4 is a mesh structure as mentioned above, themesh size is not particularly limited, though is usually preferably 80μm or smaller, more preferably approximately 15-60 μm, furtherpreferably 20-45 μm. This makes it possible to catch comparatively finebubbles without increasing the passage resistance to blood, thusproviding a relatively high bubble capturing efficiency. Where thefilter member 4 is constructed as a sheet made by crossing the warpthread 41 and the weft thread 42, it is preferable that the warp thread41 and the weft thread 42 do not extend in a direction that is the sameas the circumferential direction (extending direction) of the filtermember 4. That is, it is preferable that the warp thread 41 and the weftthread 42 do not extend parallel to a plane that is perpendicular to thelongitudinal axis or central axis of the filter member. Morespecifically, the warp thread 41 and the weft thread 42 are eachpreferably arranged in a direction that is inclined (i.e., forms anangle other than zero degrees) relative to a plane perpendicular to thelongitudinal axis or central axis of the filter member. The warp thread41 and the weft thread 42 are each preferably arranged to form apredetermined angle (e.g., 28-62 degrees) to the plane perpendicular tothe longitudinal axis of the filter member. In other words, where thefilter member 4 is constructed as a sheet formed by crossing a warpthread 41 and a weft thread 42, its mesh structure (i.e., the meshopenings forming the overall mesh structure) is a quadrilateral, e.g., asquare, a rectangle, a rhombus or a parallelogram. The quadrilateralmesh structure has a pair of opposite sides arranged in a directioninclined a predetermined angle (e.g., 28-62 degrees) to thecircumferential direction of the filter member 4. Depending upon theexpansion and contraction of the filter member 4, the angle of thequadrilateral changes in the mesh corner.

This structure helps contribute to the filter member 4 possessingelasticity (particularly appropriate elasticity) in the circumferentialdirection while still possessing sufficient strength with a relativelysimple construction. Meanwhile, the elasticity is obtained in a ratherstable manner. Due to this, tightening force (compression force) appliedto the hollow fiber membrane bundle 3 is relatively uniform and stable,contributing to the improvement of bubble-removal capability.Furthermore, such a construction prevents or suppresses the occurrenceof wrinkles (wavy concavo-convex) in the sheet at and around the joint(fusion) region 45 of the filter member 4. By the improved contact ofthe filter member 4 with the hollow fiber membrane bundle 3, it ispossible to improve the discharge efficiency of the bubbles captured bythe filter member 4 and to help ensure that the blood smoothly flows onthe outer periphery (downstream) of the filter member 4, i.e., in theblood outlet space 25.

In the event a wrinkle is formed as mentioned above, the followingdisadvantage results. First, at the inner periphery (upstream) of thefilter member, the bubbles captured by the filter member are liable tostay in a recess of the wrinkle and hence will not be easily removedtherefrom. In addition, on the outer periphery (downstream) of thefilter member, the wrinkle possibly has a projection contacting theinner surface of the housing, thereby preventing the blood from flowingsmoothly (i.e., smooth blood flow within the blood outlet space 25 inthis disclosed embodiment). It is this preferable that no wrinkles, oronly a few wrinkles, are allowed to occur.

As noted before, the filter member 4 is preferably fabricated by rollingup the sheet into a cylindrical (annular) form and joining the ends oredges thereof together in a strip form. The joint (sealing) 45 betweenthe sheet ends extends over the entire width (vertical dimension inFIG. 1) of the filter member 4, from one end 43 of the filter member 4to the other end 44 of the filter member 4 as shown in FIG. 1.

In this case, the strip-like joint region 45 preferably extends in adirection inclined at a predetermined angle (e.g. 28-62 degrees)relative to the widthwise (or circumferential) direction of the filtermember 4. As described before, when the filter member 4 is fit onto theouter periphery of the hollow fiber membrane bundle 3, the filter member4 shifts from the natural state to a state in which the filter member 4is expanded circumferentially and applied with a tension. By positioningor orienting the joint region 45 in a direction inclined relative to thewidthwise direction of the filter member 4, the possibility of a wrinkleoccurring in the sheet at and around the joint region 45 can be reduced,preferably prevented. This improves the contact of (or places without agap) the filter member 4 with the outer peripheral surface of the hollowfiber membrane bundle 3. The bubbles, caught at the filter member 4 arerelatively easily expelled through the hollow fiber membrane 311 locatedimmediately close to the inner surface of the filter member 4. Namely,the expelling efficiency can be enhanced as to, the bubbles captured atthe filter member 4.

The joint region 45 is preferably parallel (inclusive of nearlyparallel) with the extending direction of the warp thread 41 or weftthread 42 that is inclined relative to the circumferential direction ofthe filter member 4. Namely, in this embodiment, the junction region 45is parallel (inclusive of nearly parallel) with the weft thread 42 andperpendicular (inclusive of nearly perpendicular) to the warp thread 41,as shown with magnification in FIG. 1, though the embodiment is notnecessarily limited in this way. This can help reduce the possibility ofthe warp thread 41 or weft thread 42 being puckered, to reduce orprevent such a disadvantage as forming a wrinkle (concavo-convex) inpart of the sheet. This improves the contactability of (or placeswithout a gap) the filter member 4 with the outer peripheral surface ofthe hollow fiber membrane bundle 3, thus relatively easily expelling thebubbles captured at the filter member 4 through the hollow fibermembrane 311 located immediately close to the inner surface of thefilter member 4. Namely, the expelling efficiency of the bubble capturedat the filter member 4 can be improved.

The joining of the sheet edges to form the joint region 45 is notlimited in any particular manner, but is preferably by way of fusionsuch as thermal fusion, high-frequency fusion or ultrasonic fusion, oradhesion with an adhesive material. This makes it possible to relativelyeasily fabricate the filter member 4. Moreover, even if the filtermember 4, when fit onto the hollow fiber membrane bundle 3, is expanded,the joining region 45 is secured with sufficient joining strength.Accordingly, the joining region 45 is prevented from being stripped offin part thereof and the joining state is maintained without a gapthroughout the entire length of the joining region 45, thus effectivelyreducing, preferably preventing, the leak of bubbles.

The material forming the filter member 4 (the material of the warpthread 41 and the weft thread 42) can be appropriately selected, say,polyolefin such as polyamide, polyethylene or polypropylene, polyestersuch as polyethylene terephthalate, or polybutylene terephthalate,polyamide, cellulose, polyurethane, aramid fiber or the like. Of those,one or two can be used in combination (e.g., to make the warp and weftthreads 41, 42 in different compositions, make the warp thread 41 and/orthe weft thread 42 as a blended fabric, or so on). Particularly, thefilter member 4 preferably uses or includes, as its structuringmaterial, any of polyethylene terephthalate, polyethylene,polypropylene, polyamide and polyurethane in respect to an excellentantithrombotic property and clogging generated less.

The filter member 4 preferably also exhibits hydrophilic properties(possesses hydrophilicity). Namely, the filter member 4 itselfpreferably is made of a hydrophilic material or the filter member 4 havebeen subjected to a hydrophilizing processing (e.g. plasma processing).When the blood mingled with bubbles is passing, it is difficult for thebubbles to pass through, thus improving the bubble capture capability atthe filter member 4 and helping to positively prevent the bubbles fromgoing out through the blood outlet port 28. In addition, blood passageresistance is reduced at the filter member 4, thus improving theprocessing efficiency of blood.

The filter member 4 may be comprised of one sheet (particularly, a meshstructure like a screen mesh filter) or may be comprised of two or moresheets.

As mentioned previously, a gap (i.e., a blood outlet space 25) is formeddownstream of the filter member 4, between the outer peripheral surfaceof the filter member 4 and the inner peripheral surface of the housing2. This helps suppress the filter member 4 from directly (closely)contacting the inner surface of the housing 2. Thus, the blood passingthe filter member 4 is allowed to relatively easily flow down the bloodoutlet space 25 or move in a whirling manner, and then flow relativelysmoothly toward the blood outlet port 28.

A spacer may be provided in the blood outlet space 25 to help maintainor keep the gap between the filter member 4 and the housing 2.

With the filter member 4 as described above, even where bubbles exist inthe blood flowing in the blood passage 33, such bubbles can be capturedwith quite good efficiency. The bubbles captured by the filter member 4are expelled and removed through the hollow fiber membranes 311 locatedupstream of the filter member 4. Therefore, the bubbles are preventedfrom exiting through the blood outlet port 28. In this case, because ofthe close contact between the filter member 4 and the hollow fibermembrane bundle 3, bubbles tend not to stay between the filter member 4and the hollow fiber membrane bundle 3. The bubbles captured at thefilter member 4 can be expelled relatively swiftly as much as possible.

The hollow fiber membranes 311 each have a lumen forming a gas passage30 through which an oxygen-containing gas is adapted to flow. The gasinlet port 26 and the gas inlet chamber 261 constitute a gas inletlocated upstream of the gas passage 30 while the gas outlet port 27 andthe gas outlet chamber 271 constitute a gas outlet located downstream ofthe gas passage 30. The gas passage 30 serves also as a passage thatremoves the bubbles captured at the filter 4.

As described before, the heat exchange part (heat exchanger) 1B ispositioned inside the oxygenator part 1A. The heat exchange part 1Bcomprises a heat exchanger housing 5. The heat exchanger housing 5 isnearly circularly cylindrical in form, forming a blood chamber 50therein. On the right side of the heat exchanger housing 5, as seen inFIG. 2 for example, there are formed a heating medium inlet port 202 anda heating medium outlet port 203 that are both tubular in form.

As shown in FIGS. 4 and 5, arranged within the heat exchanger housing 5are a heat exchange element 54 possessing an overall circularcylindrical form, a heating medium chamber-forming member (cylindricalwall) 55 arranged along the inner periphery of the heat exchange element54 and possessing a circular cylindrical form, and a partitioning wall56 separating the inner space of the heating medium chamber-formingmember 55 into a heating medium inlet chamber 57 and a heating mediumoutlet chamber 58.

The blood chamber 50 is formed between the outer peripheral surface ofthe heat exchange element. 54 and the inner peripheral surface of theheat exchanger housing 5, allowing the blood to flow. The blood inletport 201 formed in the first header 22 has a lumen communicating withthe blood chamber 50.

The heating medium chamber-forming member 55 serves to form a heatingmedium chamber that temporarily stores the heating medium at the insideof the heat exchange element 54 and, with the heat exchanger housing 5,helps prevent the cylindrical heat exchange element 54 from deforming.

The heating medium chamber-forming member 55 and the partitioning wall56 are fixed to the heat exchanger housing 5 by, for example, fusion orbonding through an adhesive. The heating medium chamber-forming member55 and the partitioning wall 56 may be formed as separate members or asan integral one-piece member.

Openings 59 a, 59 b penetrate the wall of the heating mediumchamber-forming member 55 at diametrically opposite positions in theillustrated embodiment shown in FIG. 5. The opening 59 a communicateswith the heating medium inlet chamber 57 while the opening 59 bcommunicates with the heating medium outlet chamber 58.

The heat exchange element 54 can be in the form of a bellows-type heatexchange element (bellows tube). The bellows-type heat exchange element54 comprises a bellows-formed central portion and a cylindrical portionat each axial end. The bellows-formed central portion is comprised of amultiplicity of hollow annular projections that are parallel (inclusiveof nearly parallel) to one another so as to form a plurality of closelyarranged undulations. The inner diameter of each cylindrical end portionis equal to (inclusive of nearly equal to) the inner diameter of thebellows-formed central portion. The heat exchange element 54 is formedof a metal material such as stainless steel or aluminum, or a resinmaterial such as polyethylene or polycarbonate, for example. It ispreferable to use a metal material, such as stainless steel or aluminumfor strength considerations and heat exchange efficiency. It isparticularly preferable to construct the heat exchange element as ametal-made bellows tube in a corrugated form having a multiplicity ofrepeating concavo-convex undulations nearly orthogonal to the axis ofthe heat exchange element 54.

The heat exchanger housing 5, the heating medium chamber-forming member55 and the partitioning wall 56 can be fabricated of various materials,for example polyolefin such as polyethylene or polypropylene, an esterresin (e.g. polyester such as polyethylene terephthalate, orpolybutylene terephthalate), a styrene resin, a resin material such aspolycarbonate, various kinds of ceramics material or a metal material.

Set forth below is a description of the flow of the heating medium inthe heat exchanging part 1B of the oxygenator 1.

With reference to FIG. 5, the heating medium entering through theheating medium inlet port 202, first flows into the heating medium inletchamber 57 and then to the outer peripheral side of the heating mediumchamber-forming member 55 via the opening 59 a, thus spreading over theentire periphery of the heating medium chamber-forming member 55 andentering the multiplicity of recesses or undulations of the bellows-typeheat exchange element 54. This heats up or cools down the heat exchangeelement 54 in contact with the heating medium. Thus, heat exchange(heating or cooling) is effected with the blood entering the blood inletport 201 and flowing into the blood chamber 50 (on the outer peripheryof the heat exchange element 54).

The blood thus heat-exchanged passes through the opening 59 c, formed inan upper region of the heat exchanger housing 5, and the blood inletspace 24 in that order, then flows into the housing 2 of the oxygenatorpart 1A. The blood, entering the blood inlet space 24 spreads our overthe entire circumference of the blood inlet space 24 where it flows intothe blood passage 33 through various points for gas exchange.

Meanwhile, the heating medium which has been used to perform heating orcooling enters the heating medium outlet chamber 58 through the opening59 b and then exits at the heating medium outlet port 53.

It is to be noted that while the embodiment described above includes theheat exchanging part 1B, the heat exchanging part 1B is not required.

Set forth below is a description of the blood flow in the oxygenator 1according to this embodiment.

In the oxygenator 1, the blood entering at the blood inlet port 201flows into the blood chamber 50 (i.e., between the inner surface of theheat exchanger housing 5 and the heat exchange element 54) where itcontacts the outer surface of the plurality of hollow annularprojections or undulations of the heat exchange element 54, thuseffecting heat exchange (heating or cooling). The blood, heat-exchangedin the blood chamber 50, passes through the opening 59c and spreads intothe blood inlet space 24. The blood flows downstream (i.e., toward theouter periphery) along the blood passage 33.

Meanwhile, the gas (oxygen-containing gas) supplied through the gasinlet port 26 enters the gas inlet chamber 261 and is distributed fromthe gas inlet chamber 261 into the gas passages 30 formed by the lumensof the hollow fiber membranes 311. After passing through the gaspassages 30, the gas is collected in the gas outlet chamber 271 andallowed to exit at the gas outlet port 27. The blood flowing along theblood passage 33 contacts the surfaces of the hollow fiber membranes 311so that gas exchange (oxygenation, removal of carbon dioxide) isachieved with the gas flowing through the gas passages 30.

In the event bubbles are present in the blood, such bubbles are capturedby the filter member 4 and are not allowed to exit to the downstreamside of the filter member 4. The bubbles, captured at the filter member4, enter the lumens (gas passages 30) of the hollow fiber membranes 311located upstream of and adjacent to the filter member 4 via themultiplicity of fine pores formed in the material (walls) of the hollowfiber membranes 311. The bubbles entering the lumens of the hollow fibermembranes 311 are discharged at the gas outlet port 29.

The blood thus subjected to gas exchange, and also subjected to bubbleremoval by virtue of the filter member 4, flows into the blood outletspace 25 and toward the blood outlet port 28, with the blood exitingthrough the blood outlet port 28.

The oxygenator 1 described above as one embodiment is preferablyconstructed so that the surfaces which are to contact blood (e.g., theinner surface of the housing 2, the inner surface of the heat exchangerhousing 5, the surface of the heating medium chamber-forming member 55,the surface of the partitioning wall 56, the fixed region 7, and thesurfaces of the partitioning walls 8, 9 facing the blood passage 33) areantithrombotic. Such an antithrombotic surface can be formed by coatingor applying an antithrombotic material onto the surfaces. Theantithrombotic material may be heparin, urokinase, HEMA-St-HEMAcopolymer, poly-HEMA or the like.

The blood flow rate at the blood inlet port 28 of the oxygenator 1 isnot limited to any specific value as it will vary, at least in part,depending upon, for example, the patient's physique and the operationalscheme. However, as examples, a blood flow rate of 0.1-2.0 L/min ispreferred in an infant or child, a blood flow rate of 2.0-5.0 L/min ispreferred for a child in elementary or middle school, and a blood flowrate of 3.0-7.0 L/min is preferred for adults.

The gas flow rate at the gas inlet port 26 is also not particularlylimited as it will diff depending upon, for example, the patient'sphysique and the operational scheme. However, byway of example, a gasflow rate of 0.05-4.0 L/min is preferred for an infant or child, a gasflow rate of 1.0-10.0 L/min is preferred for a child in elementary ormiddle school, and a gas flow rate of 1.5-14.0 L/min is preferred for anadult.

The oxygen concentration in the gas supplied through the gas inlet port26 is not limited to a specific value because it will differ dependingupon, for example, the metabolic amount of oxygen/carbon-dioxide gas ofthe patient undergoing the medical procedure. Nevertheless, as anexample, the oxygen concentration in the gas can be on the order of40-100%.

The maximum continuous operation time of the oxygenator 1 will alsodiffer depending upon the patient's condition and the operationalscheme. However, a maximum continuous operation Lime of the oxygenator 1is usually approximately 2-9 hours. The maximum continuous operationtime of the oxygenator 1 will rarely amount to a time as long as nearly10 hours.

Despite its relatively small size, the oxygenator 1 disclosed here has arelatively high performance, i.e., a relatively high gas exchangecapability without outputting bubbles, and also has a relativelyexcellent sustainability in performance. Accordingly, it can fully copewith a relatively long time of operation, hence being broad in itsapplications.

FIG. 8 shows an embodiment in which a part of the housing of theoxygenator possesses a modified shape or configuration. In theembodiment shown in FIG. 8, the housing 21A is provided with a passageenlargement 282. The passage enlargement 282 is comprised of a firstenlargement 282A and a second enlargement 282B continuing from the firstenlargement 282A. The first enlargement 282A is located on the upstreamside of the second enlargement 282B. The first enlargement 282A A iscomprised of a recess formed in the inner peripheral surface of thecylindrical housing in a region surrounding the blood outlet port 28 andextending axially along the entire length of the cylindrical housing. Inthe illustrated embodiment, this recess forming the first enlargement282A possesses a constant width along the entire axial extent of thehousing.

In addition, as can be seen from a comparison of FIGS. 5 and 8, theblood outlet port is moved radially outwardly to thereby form the secondenlargement 282B.

By virtue of the passage enlargement, the flow velocity of the bloodpassing through the filter is reduced, thereby capturing bubbles at thefilter with greater ease.

It is to be recognized that the principles, preferred embodiments andmodes of operation have been described in the foregoing specification,but the invention which is intended to be protected is not to beconstrued as limited to the particular embodiments disclosed. Further,the embodiments described herein are to be regarded as illustrativerather than restrictive. Variations and changes may be made by others,and equivalents employed, without departing from the spirit of thepresent invention. Accordingly, it is expressly intended that all suchvariations, changes and equivalents which fall within the spirit andscope of the present invention as defined in the claims, be embracedthereby.

What is claimed is:
 1. A method of making a filter arrangementconfigured to be positioned in a housing of an oxygenator, comprising:rolling a sheet of filter material into a cylindrical filter member; andplacing the cylindrical filter member over an outer periphery of ahollow fiber membrane bundle to closely contact the outer periphery ofthe hollow fiber membrane bundle, wherein the hollow fiber membranebundle is comprised of a plurality of integrated hollow fiber membranesthat are formed of polymer material and are transmissive to gas.
 2. Themethod of claim 1, wherein the cylindrical filter member possessescircumferential elasticity allowing an inner circumference of thecylindrical filter member to be increased from a natural non-expandedstate prior to placement over the outer periphery of the hollow fibermembrane bundle to an expanded state in which the inner circumference ofthe cylindrical filter member is increased when placed over the outerperiphery of hollow fiber membrane bundle.
 3. The method of claim 1,further comprising joining opposite edges of the shoot material togetherat a joint after rolling the sheet of filter material into thecylindrical filter member.
 4. The method of claim 3, wherein theopposite edges of the sheet material are joined together at the joint byfusion.
 5. The method of claim 3, wherein the opposite edges of thesheet material are joined together at the joint by adhesive bonding. 6.The method of claim 3, wherein the joint extends in a direction inclinedrelative to a widthwise direction of the filter member.
 7. The method ofclaim 1, wherein the shoot of filter material is formed of a hydrophylicmaterial.
 8. The method of claim 1, wherein the sheet of filter materialis a mesh.
 9. The method of claim 1, wherein the sheet of filtermaterial is formed by crossing a warp thread and a weft thread with eachother.
 10. The method of claim 9, wherein the warp threads or the weftthreads are arranged in the sheet of filter material such that, when thecylindrical filter member is formed, the warp threads or the weftthreads are inclined at an angle other than zero degrees relative to aplane that is perpendicular to a longitudinal axis of the cylindricalfilter member.
 11. A method of making a filter arrangement configured tobe positioned in a housing of an oxygenator, comprising: rolling a sheetof filter material into a cylindrical filter member; and placing thecylindrical filter member over an outer periphery of a hollow fibermembrane bundle to closely contact the outer periphery of the hollowfiber membrane bundle, wherein the cylindrical filter member possessescircumferential elasticity allowing an inner circumference of thecylindrical filter member to be increased from a natural non-expandedstate prior to placement over the outer periphery of the hollow fibermembrane bundle to an expanded state in which the inner circumference ofthe cylindrical filter member is increased when placed over the outerperiphery of hollow fiber membrane bundle.
 12. The method of claim 11,further comprising joining opposite edges of the sheet material togetherat a joint after rolling the sheet of filter material into thecylindrical filter member.
 13. The method of claim 12, wherein theopposite edges of the sheet material are joined together at the joint byfusion.
 14. The method of claim 12, wherein the opposite edges of thesheet material are joined together at the joint by adhesive bonding. 15.The method of claim 12, wherein the joint extends in a directioninclined relative to a widthwise direction of the filter member.
 16. Themethod of claim 11, wherein the sheet of filter material is formed of ahydrophylic material.
 17. The method of claim 11, wherein the sheet offilter material is a mesh.
 18. The method of claim 11, wherein the sheetof filter material is formed by crossing a warp thread and a weft threadwith each other.
 19. The method of claim 18, wherein the warp threads orthe weft threads are arranged in the sheet of filter material such that,when the cylindrical filter member is formed, the warp threads or theweft threads are inclined at an angle other than zero degrees relativeto a plane that is perpendicular to a longitudinal axis of thecylindrical filter member.